This proposal describes the in vitro and in vivo testing and further development of a therapeutic and diagnostic test for patients at risk for respiratory distress syndrome of the newborn. This disease is in large part caused by a lack of pulmonary surfactant, a phospholipid-protein complex essential for normal lung function. Respiratory Distress Syndrome (RDS) is the leading cause of neonatal mortality and morbidity. Using recombinant DNA technology we are producing large amounts of the protein component of human surfactant. This protein will be purified and combined with a defined mixture of synthetic lipids which will be used to treat infants having this disease. The other portion of this proposal involves further development of an immunodiagnostic test based on quantitation of the protein component of surfactant. The test will be carried out on amniotic fluids obtained during pregnancy and will be efficacious in predicting fetal lung maturity since it is based on a specific protein rather than the non-specific lipid components. In combination these two products, a diagnostic test and a therapeutic, will provide a safe effective combination to treat neonatal RDS.